Rainwater not only doesn't contain chlorine, salts and fluoride which can harm plants, it also is higher in nitrogen picked up from the atmosphere. Nitrogen is the most common fertilizer applied to fields and lawns.
Collecting rainwater can payback huge dividends in your landscapes, with the added nutrient and especially during times of little rainfall or mild drought.
Abundant Design will show you ways to use and collect this valuable superpowered water, with rain barrels and much, much more!
See also http://abundantdesigniowa.blogspot.com/2014/07/rain-barrels-are-great-but.html
Rain Barrels & Systems pricing varies with scope
Rain Barrels starting at $135+tax & installation
Basic Sediment Filter (add-on)
Custom Overflow (add-on)
Rain Harvesting Earthworks
Rain Gardens & BioSwales